x86-64: Fix CFI data for interrupt frames

The patch titled "x86: Don't use frame pointer to save old stack
on irq entry" did not properly adjust CFI directives, so this
patch is a follow-up to that one.

With the old stack pointer no longer stored in a callee-saved
register (plus some offset), we now have to use a CFA expression
to describe the memory location where it is being found. This
requires the use of .cfi_escape (allowing arbitrary byte streams
to be emitted into .eh_frame), as there is no
.cfi_def_cfa_expression (which also cannot reasonably be
expected, as it would require a full expression parser).

Signed-off-by: Jan Beulich <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/dwarf2.h

···
 #define CFI_REMEMBER_STATE	.cfi_remember_state
 #define CFI_RESTORE_STATE	.cfi_restore_state
 #define CFI_UNDEFINED		.cfi_undefined
+#define CFI_ESCAPE		.cfi_escape
 
 #ifdef CONFIG_AS_CFI_SIGNAL_FRAME
 #define CFI_SIGNAL_FRAME	.cfi_signal_frame
···
 #define CFI_REMEMBER_STATE	cfi_ignore
 #define CFI_RESTORE_STATE	cfi_ignore
 #define CFI_UNDEFINED		cfi_ignore
+#define CFI_ESCAPE		cfi_ignore
 #define CFI_SIGNAL_FRAME	cfi_ignore
 
 #endif

arch/x86/kernel/entry_64.S

···
 1:	incl PER_CPU_VAR(irq_count)
 	jne 2f
 	mov PER_CPU_VAR(irq_stack_ptr),%rsp
-	EMPTY_FRAME 0
+	CFI_DEF_CFA_REGISTER	rsi
 
 2:	/* Store previous stack value */
 	pushq %rsi
+	CFI_ESCAPE	0x0f /* DW_CFA_def_cfa_expression */, 6, \
+			0x77 /* DW_OP_breg7 */, 0, \
+			0x06 /* DW_OP_deref */, \
+			0x08 /* DW_OP_const1u */, SS+8-RBP, \
+			0x22 /* DW_OP_plus */
 	/* We entered an interrupt context - irqs are off: */
 	TRACE_IRQS_OFF
 	.endm
···
 	subq $ORIG_RAX-RBP, %rsp
 	CFI_ADJUST_CFA_OFFSET ORIG_RAX-RBP
 	SAVE_ARGS_IRQ
-	PARTIAL_FRAME 0
 	call \func
 	.endm
 
···
 
 	/* Restore saved previous stack */
 	popq %rsi
-	leaq 16(%rsi), %rsp
-
+	CFI_DEF_CFA_REGISTER	rsi
+	leaq ARGOFFSET-RBP(%rsi), %rsp
 	CFI_DEF_CFA_REGISTER	rsp
-	CFI_ADJUST_CFA_OFFSET	-16
+	CFI_ADJUST_CFA_OFFSET	RBP-ARGOFFSET
 
 exit_intr:
 	GET_THREAD_INFO(%rcx)